Disk-type brakes, because of their planar braking surfaces have the advantage of having straight-line characteristics by contrast with the nonlinear characteristics of drum-type brakes, so that in use, disk-type brakes can avoid swerving of the vehicle, even in the case of heavily loaded heavy-duty vehicles. For this reason segmental disk brakes have been widely employed in recent years for passenger automobiles and the like. Drum-type brakes because of the nature of the heat dissipation therefrom by convection, are generally superior to such segmental disk brakes on thermal grounds. As a result, for heavy duty vehicles operating under heavy loads, drum-type brakes have been predominantly employed. If, for example, the braking system provides segmental disk brakes at the front axle of such a vehicle, it is necessary to ensure that the vehicle will have retarders, engine braking systems or auxiliary brakes to provide the additional braking capacity which may be necessary, at a considerable cost, increasing vehicle weight and providing a challenge to the reliability of the brake system.
A full-lining brake, by contrast to the segmental disk brakes described above, however, for a given weight and fabrication cost, has thermal advantages over drum-type brakes as can be demonstrated readily in road tests. For example, in braking over a downgrade of 10% at a speed of 60 km/h, a two-surface full lining brake with a brake housing having radial heat dissipating ribs in less than a minute of braking time can achieve a thermal equilibrium between the braking heat generated and the convective heat dissipated at a temperature range which does not give rise to significant brake wear for present-day standard linings. By contrast, a drum-type brake does not, under similar conditions, reach a steady state temperature even after 10 minutes and at such a brake duration, will reach the 700.degree. C. maximum which such a brake can tolerate. A segmental disk brake of the type widely used in automotive vehicles under similar conditions can reach a temperature of 1000.degree. C.
Without significant increase in weight, full lining brakes can have their continuous braking effect increased by providing a direct compressed air actuation with four brake surfaces per brake and each wheel brake provided with two brake circulations. Such systems are described, for example, in German Patent Documents DE 37 05 911 and DE 37 256 24. These systems, however, are not fully satisfactory because they do not provide for parking brake or emergency or auxiliary braking action, i.e. for vehicle-locking or like brake action.